1.2 Standard (Conventional) Motor Control Centre (MCC):
a) Integrated motor control center is a group of motor control starters equipped
with protection hardware and located near a process building. All the motor
starters are grouped in a single panel board, installed in an electrical room
which is neat & clean and dust proof.
b) The panel board contains individual starter for individual motor consisting
a set of hardware like switch fuse unit, contactor, bimetal thermal over load
relays, local start/stop button and indication lamps on the front door of the
starter.
c) Integrated motor control centre is used for group process control function
where a set of equipment are required to operate in sequential mode to per
form a certain process task. In this case, process activity of equipment is inter
dependent to its precede and successor equipment and it cannot perform its
function alone.
d) The motor is started from central control station in group mode to start the
process. The motor control station takes care of motor protection only. How
ever, process is controlled by operator through DCS system. The central
processing unit is with pre-built up programmed performs the process inter
lock. HMI (human machine interface) is used to interface between machine
(through DCS) and plant operator.
e) All motor starter signals are interfaced with DCS system with centrally located
input/output interface stations. This I/O device is capable to interface digital
signals and analogue signal which are used for process interlocking and
controlling functions.
f) Local operation of individual equipment is only envisaged for maintenance
and inspection purpose. Always remote operation is envisaged for process
operation mode through distributed control system.
g) The integrated control system also offers motor thermal, single phase and
short circuit protections like individual control starters. However, group control
is possible through DCS system.
h) The integrated motor control station has following key features:
- The system is costlier than individual control station by 20% but cheaper
than intelligent control system, - The system is a little bit complex than individual starter to operate and
maintain, - It needs good skill level of operator for operation and maintenance,
- Skilled mechanic is required for fault tracing and its rectification during
normal operation, - Cost of maintenance is high as compared to individual starter,